Growing polar semiconductors, such as III-V and II-VI compound semiconductors, on nonpolar substrates, such as silicon (Si) or germanium (Ge), is desirable for the implementation of a variety of integrated electronic and optical applications. Such applications include, for example, optical interconnects between integrated circuit chips, optical computing and photonic switching. It is, however, difficult to grow compound semiconductors on nonpolar substrates. The principal reason for this difficulty is that there are no preferential bonding sites for initial growth on the nonpolar substrate for the cations and anions of the compound semiconductor. As a result, some growth may begin in the cation plane, and some in the anion plane. This is referred to as antiphase disorder. Further, differences in the lattice structure of certain semiconductors, such as gallium arsenide (GaAs) and Si, for example, present an additional impediment to satisfactory growth. Antiphase disorder and lattice mismatch may result in both structural and electrically active defects.
The difficulty with growing compound semiconductors, in particular GaAs, on nonpolar substrates, has been addressed in the prior art. See Fischer et al., "Growth and Properties of GaAs/AlGaAs on Nonpolar Substrates Using Molecular Beam Epitaxy," J. Appl. Phys. 58(1) at 374-81 (1985); Biegelsen et al., "Heteroepitaxial Growth of Polar Semiconductors on Non-Polar Substrates," Mat. Sci. Eng. B14(3) at 317-331 (1992); Harris et al., "The Nucleation and Growth of GaAs on Si," Mat. Res. Soc. Symp. Proc., Vol. 91 at 3-14 (1987); Tran et al., "Growth and Characterization of InP on Silicon by MOCVD," J. Crys. Grwth. 121(3) at 365-72 (1992); Sporken et al., "Molecular Beam Epitaxy of CdTe on Large Area Si&lt;loO&gt;," J. Vac. Sci. Tech. B 9(3) at 1651-55 (1991). All articles referenced in this specification are incorporated herein by reference.
One approach for growing compound semiconductors on nonpolar substrates is to angle or tilt the substrate off the standard &lt;100&gt; orientation. See Harris et al. The designation "&lt;100&gt;" is known as a Miller indice. It may be used to describe the orientation of a planar surface. The &lt;100&gt; surface refers to a surface which lies along a face of a cubic lattice structure, and this is the standard orientation for substrates such as silicon. However, there are problems associated with using "off-axis" silicon substrates for integrated electronics. In particular, it has been found that device performance of metal oxide semiconductor (MOS) transistors formed in off-axis wafers is affected by this surface orientation. See Chung et al., "The Effects of Low-Angle Off-Axis Substrate Orientation on Mosfet Performance and Reliability," IEEE Trans. Electr. Dev. 38(3) at 627-33 (1991).
Others have explored the use of superlattice buffer layers to minimize lattice mismatch between the substrate and the compound semiconductor. To achieve growth of GaAs on Si, Sakai et al., Mater. Res. Soc. Symp. Proc., Vol. 67 at 15 (1986) used a series of layers, beginning with a GaP layer that is lattice matched to Si, then deposited successive GaP/GaAsP and GaAsP/GaAs superlattice layers. Testing of devices, such as a laser, formed utilizing superlattice buffered GaAs/Si suggests that significant defects are still present. See Harris et al.
Accordingly, there is a need for a method to grow polar semiconductors on a standard orientation &lt;100&gt;, nonpolar substrate.